The use of an electrical junction or outlet box to accommodate electrical cable terminations is well known in the art. These boxes typically house electrical components, such as electrical receptacles, jacks and plugs and other devices. The junction box permits the electrical cables to either pass through or connect to the electrical components housed inside the box. In certain applications, these junction boxes are used in floor installations, and are referred to as floor boxes. Electrical cable distribution takes place beneath the surface of the floor and the junction boxes are designed to be supported within a poured concrete floor. One of the problems in positioning a floor box is that the installer must assure that the top of the floor box is both flush and level with the top of the poured floor in which it is set. Variations in the thicknesses of poured floors require a user to either stock several types of floor boxes with different dimensions or modify floor boxes to the requirements of a particular application.
In the prior art, it is known to provide floor boxes which are set in poured concrete floors and then sawed off to accommodate the depth of the poured floor. Examples of these cuttable floor boxes are shown in U.S. Pat. No. 3,343,704 to Terry and U.S. Pat. No. 5,466,886 to Lengyel et al. However, these cuttable floor boxes have certain disadvantages. The cuttable floor boxes typically have an open end and thus require a separate cover to protect the interior of the box from debris and extraneous concrete during pouring of the concrete floor. Furthermore, many of these cuttable floor boxes require complicated assemblies to assure that the terminations housed at the upper end of the box are level with the concrete floor. Additionally, many electrical standards, such as the National Electrical Code (NEC), require floor boxes that accommodate multiple services (e.g., power and communication services) be designed to maintain physical separation between the various services within the box.
In many floor applications, the junction box is positioned on a deck and concrete is poured over the deck to form the floor. The deck typically includes ducts, conduits or corrugations for the passage of the cables under the floor. In these applications, the junction box is positioned on the deck and connected to the duct, conduit or corrugations prior to pouring the concrete. Once the box is properly positioned, the concrete is poured onto the deck and around the junction box to form a concrete floor.
In order to accommodate variations in the poured concrete floor thickness, the junction box is typically constructed so that the upper end of the box extends above the level of the poured concrete floor. Once the concrete floor has set, the installer cuts away the portion of the box extending above the surface of the floor so that the top of the box is flush with the surface of the poured concrete floor. The cutting may be accomplished by hand sawing the extending portion of the box. During this process, especially with respect to plastic floor boxes, the sides of the box may flex under the force of the saw. This flexing can create a space between the outside walls of the box and the surrounding concrete floor. Loose pieces of concrete and other debris in the area have a tendency to back-fill into the space between the flexed wall of the box and the concrete floor. As a result of the collection of debris in the space, the wall of the box assumes a permanent internal bow or deformation, which can make internal adjustment of the box difficult to accomplish. Also, internal bowing reduces the useable interior space and makes it more difficult for the installer to make connections inside the box. This problem is especially prevalent in plastic rectangular floor boxes where the elongate side walls have a greater tendency to bow or flex either when sawed or due to the force of the poured concrete on the outside wall.
At the present time, there is no approved method for the installation of electrical boxes in thick concrete slabs, such as post-tensioned slabs. In some cases, the installer glues and/or tapes the open ends of two conventional boxes together and places them on the ground. This is primarily so that the length of the joined boxes is greater than the thickness of the concrete slab. It also serves to prevent concrete from entering the interior of the box. After the concrete is poured and set, the closed end of the box protruding from the top of the concrete is cut flush with the top surface of the slab.
It is, therefore, desirable to provide a floor box for installation in a poured concrete floor which can easily be modified to accommodate concrete floors of different thicknesses. It is also desirable to provide a floor box that can be securely anchored within a poured concrete floor without bowing or flexing of the side walls due to cutting the upper end of the box flush with the floor. Moreover, there is a need for an electrical box extension that can be used with concrete floors of different depths. Further, there is a need for a floor box with a structure that prevents concrete from entering the box.